Method and system for antenna selection diversity with biasing

ABSTRACT

A signal quality metric is determined for each of multiple signal paths. Each of the signal paths corresponds to a respective antenna. The determined signal quality metric is modified for one or more signal paths. A subset of the signal paths is selected for receiving a signal based at least in part on the determined signal quality metrics. The selecting is biased based at least in part on the modified signal quality metrics.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application makes reference to, claims priority to, and claims thebenefit of U.S. application Ser. No. 12/725,060 filed Mar. 16, 2010,which application makes reference to, claims priority to, and claims thebenefit of U.S. application Ser. No. 10/810,186 filed Mar. 26, 2004,which application makes reference to, claims priority to, and claims thebenefit of U.S. Provisional Application Ser. No. 60/547,366 filed Feb.24, 2004 and entitled “Method and System for Antenna Selection Diversityand Dynamic Gain Control.”

This application makes reference to:

-   U.S. Utility application Ser. No. 10/810,462 filed Mar. 26, 2004.-   U.S. Utility application Ser. No. 10/810,433 filed Mar. 26, 2004.-   U.S. Utility application Ser. No. 10/810,408 filed Mar. 26, 2004.

The above stated applications are hereby incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to wireless communication.More specifically, certain embodiments of the invention relate to amethod and system for antenna selection diversity with biasing.

BACKGROUND OF THE INVENTION

In a wireless communication system a data stream will most likelyexperience multiple reflections (multipath) while propagating betweenthe transmitter and the receiver. Multipath fading implies that multiplecopies of the transmitted signal follow different paths and reach thereceiving antenna with different time delays. In such cases, thereceived signal strength at a given time is the result of destructiveand constructive interference of the multiple paths arriving fromdifferent directions. Destructive interference may degrade theperformance of the detector and, therefore, it may adversely affects thesystem capacity. However, by using multiple antennas at the receiver andwith appropriate digital signal processing methods, a multipath may beexploited to enhance the performance and robustness of the receiver andto increase the reliability of the communications link. The receivingantennas may need to be spaced sufficiently far apart so that the signaleach antenna sees may not be correlated with the signals seen by theother antennas. Selection diversity may be utilized in mitigatingmultipath fading.

The algorithm for selection diversity is based on selecting the bestsignal among all the signals detected at the receiver antennas. If P_(i)denotes the power estimated at antenna i at the receiver, the selectiondiversity scheme may select antenna jas the receive antenna ifP_(j)>P_(i), i≠j. Higher accuracy in estimating the powers P_(i) mayresult in higher probability of the right receive antenna beingselected, and in better performance of the selection diversity scheme.Factors that affect the accuracy of the power estimates P_(i) mayinclude the presence of impairments, such as noise, transients andoffsets, for example.

Impairments, such as noise, transients and offsets, corrupt the powerestimates P_(i) and may result in misestimations of the power during anantenna selection process. Such misestimations of power may lead to theselection of antenna j, for example, as the receive antenna, even ifP_(j)<P_(i) for some other antenna i.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present invention asset forth in the remainder of the present application with reference tothe drawings.

BRIEF SUMMARY OF THE INVENTION

Certain embodiments of the invention may be found in a method and systemfor choosing at least one signal path for an antenna system of areceiver, transmitter and/or a transceiver. Aspects of the method mayinclude determining a signal quality metric for each of a plurality ofsignal paths and modifying the signal quality metric for each of theplurality of signal paths. At least one signal path may be selectedbased on at least one modified signal quality metric. At least one ofthe signal paths may be cycled through. The signal quality metric may bebiased, increased by a fixed amount and/or by a predetermined amountand/or dynamically changed for each of the plurality of signal paths.The signal quality metric may be decreased for each of the plurality ofsignal paths by a fixed amount and/or a predetermined amount.

A signal path with a signal quality metric greater than at least onemodified signal quality metric may be selected. A signal path with asignal quality metric less than at least one modified signal qualitymetric may be selected. The signal quality metric may include, but isnot limited to, a power level characteristic, a packet error ratecharacteristic, a bit error rate characteristic, a propagation channelcharacteristic, and/or an interference level characteristic. One or moreof the signal paths may comprise an antenna and each of the signal pathsmay include a receive signal path and/or a transmit signal path.

Another embodiment of the invention may provide a machine-readablestorage, having stored thereon, a computer program having at least onecode section executable by a machine, thereby causing the machine toperform the steps as described above for choosing at least one signalpath.

Aspects of the system for choosing at least one signal path may includeat least one processor that determines a signal quality metric for eachof a plurality of signal paths. The at least one processor may modifythe signal quality metric for each of the plurality of signal paths andmay select at least one signal path based on at least one modifiedsignal quality metric. The at least one processor may cycle through atleast one of the signal paths and, and/or increase the signal qualitymetric for each of the plurality of signal paths by a fixed amountand/or by a predetermined amount. The at least one processor maydynamically change and/or decrease the signal quality metric for each ofthe plurality of signal paths by a fixed and/or a predetermined amount.The at least one processor may select a signal path with a signalquality metric greater than or less than at least one modified signalquality metric. The signal quality metric may include a power levelcharacteristic, a packet error rate characteristic, a bit error ratecharacteristic, a propagation channel characteristic, and/or aninterference level characteristic. One or more of the signal paths maycomprise an antenna and each of the signal paths may include a receivesignal path and/or a transmit signal path.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a diagram of an exemplary receiver system that may beutilized in connection with selection diversity with dynamic gaincontrol, in accordance with an embodiment of the invention.

FIG. 1B is a diagram of an exemplary antenna switch in a receiver systemthat may be utilized with selection diversity with dynamic gain control,in accordance with an embodiment of the invention.

FIG. 2A illustrates exemplary received powers by different antennas in areceiver system, in accordance with an embodiment of the invention.

FIG. 2B illustrates exemplary antenna dwell times, signal gain, andantenna selection in a receiver system in connection with selectiondiversity with dynamic gain control, in accordance with an embodiment ofthe invention.

FIG. 3A illustrates exemplary received powers by different antennas in areceiver system, in accordance with an embodiment of the invention.

FIG. 3B illustrates exemplary antenna dwell times, signal clipping, andantenna selection in a receiver system in connection with selectiondiversity with dynamic gain control, in accordance with an embodiment ofthe invention.

FIG. 3C illustrates exemplary antenna dwell times, dynamic gain control,and antenna selection, in accordance with an embodiment of theinvention.

FIG. 4A illustrates exemplary received powers by different antennas in areceiver system, in accordance with an embodiment of the invention.

FIG. 4B illustrates exemplary antenna dwell times, dynamic gain control,and antenna selection, in accordance with an embodiment of theinvention.

FIG. 5 is a flow chart illustrating exemplary steps that may be utilizedin a receiver system for antenna selection with dynamic gain control, inaccordance with an embodiment of the invention.

FIG. 6 is a graphical depiction of antenna selection without a bias,which may be utilized in connection with an embodiment of the invention.

FIG. 7 is a graphical depiction of antenna selection with bias, inaccordance with an embodiment of the invention.

FIG. 8 is a flow diagram of an exemplary method for selecting a signalpath, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain aspects of the present invention may be found in a method andsystem for choosing at least one signal path. For each of a plurality ofsignal paths, a signal quality metric may be determined. The signalquality metric may be modified for each of the signal paths, and asignal path may be selected based on at least one modified signalquality metric. Signal paths may be cycled through and the signalquality metric may be biased for each of the signal paths. The signalquality metric may also be dynamically changed for each signal path,increased or decreased by a fixed amount and/or by a predeterminedamount. A signal path with a signal quality metric greater than, or lessthan, a modified signal quality metric may be selected. The signalquality metric may include a power level characteristic, a packet errorrate characteristic, a bit error rate characteristic, a propagationchannel characteristic, and/or an interference level characteristic. Oneor more of the signal paths may comprise an antenna and each of thesignal paths may include a receive signal path and/or a transmit signalpath.

Certain other embodiments of the invention may also be found in a methodand system for antenna selection diversity with dynamic gain control.Wireless communication systems may utilize receivers with multipleantennas to enhance the performance and robustness of the receiver andto increase the reliability of the communications link. Certain aspectsof the method may comprise dwelling on at least one of several antennasin a receiver system in order to select a portion of those antennas forsignal processing, determining a gain, and determining a signal qualitymetric for the dwelled-on antennas. The power may be an estimatedreceived power or it may be a received power. Selecting the portion ofantennas that may be used for signal processing may be based on thegain, the estimated signal quality metric, and/or the received signalquality metric of the dwelled-on antennas.

A starting antenna may be selected from the antennas in the receiversystem based on a predetermined criteria, random selection, and/or oninformation of which dwelled-on antennas or portion of dwelled-on havebeen selected for signal processing in the past. A starting gain for thestarting antenna may be determined by using an automatic gain control.

Other antennas in the receiver system may be selected for dwelling basedon a predetermined criteria. For each of the dwelled-on antennas, a gainmay be determined dynamically based on the gain, the signal qualitymetrics, and/or on at least one of the power coupling parameters thatmay be measured between the antenna switch outputs in the receiver. Thesignal quality metrics may be an estimated received power, a receivedpower, a signal-to-noise ratio, a bit error rate, a packet error rate, apropagation channel characteristic, an/or a channel interference.Selecting a portion of the dwelled-on antennas for signal processing inthe current information frame may be based on a comparison against aspecified range of levels for at least one signal quality metric.

FIG. 1A is a diagram of an exemplary receiver system that may beutilized in connection with selection diversity with dynamic gaincontrol, in accordance with an embodiment of the invention. Referring toFIG. 1A, the receiver system 100 may comprise at least one antenna 102,an antenna switch 104, a processor 106, and a memory 108. There may beas many as M antennas 102 coupled to the antenna switch 104. The antenna102 may be part of an independent antenna array of antennas coupled tothe antenna switch 104, may be one of several individual antennascoupled to the antenna switch 104, and/or may be one of severalintegrated individual antennas and/or may be part of an integrated arrayof antennas coupled to the antenna switch 104. The antenna switch 104may be a mechanical, electronic, electromechanical, and/ormicroelectromechanical (MEM) switch. The processor 102 may be a hardwareresource, a core processor, a coprocessor, a digital signal processor,or a microcontroller. The memory 108 may be an external memory, anembedded memory, a shared memory, or a main memory. The memory 108 maybe an SRAM and/or DRAM type memory.

The incoming wireless signal may be received by at least one antenna102. The antenna switch 104 may select the antenna channel of anyantenna 102. The processor 106 may notify the antenna switch 104 whichantenna channel corresponding to a particular antenna 102 to select. Theprocessor 106 may be utilized to determine which antenna 102 may be thestarting antenna, to determine which antenna 102 to select next, todetermine the dwell time in each selected antenna, to detect and decodethe incoming signal, and to amplify or apply a gain to the signal. Theprocessor 106 may apply gain to the signal from an antenna channel byutilizing an automatic gain control (AGC) or by determining a specificgain to apply. The processor 106 may be utilized to determine theestimated power of the signal, to determine a signal-to-noise ratio, todetermine a packet-error-rate or bit-error-rate, to transfer informationto and from memory 108, and to determine statistics based on informationfrom several transmitted frames stored in memory 108. The memory 108 maybe utilized to store information processed by the processor 106 that maybe associated with any antenna 102 in any number of transmitted frames.

In operation, the processor 106 may notify the antenna switch 104 whichantenna 102 may be used as the starting antenna. The processor 106 maydetermine which antenna 102 to use for the starting antenna based oninformation from preceding frames that may be stored in memory 108. Theantenna switch 104 may select the antenna channel that corresponds tothe selected antenna 102. The processor 106 may dwell on the startingantenna until it detects an incoming signal. Once the signal isdetected, an AGC may be applied to obtain a sufficiently strong signalfor decoding. The processor 106 may determine the estimated receivedpower for the starting antenna and may store the value in memory 108.The processor 106 may then notify the antenna switch 104 to select thenext antenna 102 for detection. The processor 106 may determine whichantenna 102 to use as the next antenna based on information frompreceding frames that may be stored in memory 108. The antenna switch104 may select the antenna channel that corresponds to the next antenna.The processor 106 may dwell on the next antenna and apply apredetermined gain because the dwell time may be insufficient for an AGCto run its full operation. The processor 106 may determine the estimatedreceived power for the next antenna and may store the value in memory108. A similar procedure may be carried out with the remaining antennasin receiver system 100. With the exception of the starting antenna, apredetermined gain may be applied to all the other antennas becausedwell time in all but the starting antenna is limited. The processor 106may determine an estimated received power for all antennas in receiversystem 100 and store the values in memory 108. The processor 106 mayselect the best antenna for decoding by selecting the highest estimatedreceived power to determine the antenna 102 which has the strongestsignal. The processor 106 may then notify the antenna switch 104 toselect the antenna channel that corresponds to the antenna 102 with thestrongest signal for decoding. The processor 106 may then detect anddecode the signal from the selected best antenna and may storeinformation associated with the antenna 102 it selected as the bestantenna for the current frame.

FIG. 1B is a diagram of an exemplary antenna switch in a receiver systemthat may be utilized with selection diversity with dynamic gain control,in accordance with an embodiment of the invention. Referring to FIG. 1B,in this exemplary diagram, the selector 110 in antenna switch 104 may beconfigured to connect antenna 1 to processor 106. In this case, theincident power Q₁ in antenna 1 is received by processor 106. Moreover,because the isolation between antenna channels 112 in antenna switch 104is not perfect, in this configuration the processor 106 may alsoreceive, when detecting a signal in antenna 1, part of the incidentpowers Q₂ through Q_(M) received by antennas 2 through M. The amount ofeach incident power Q₂ through Q_(M) from antennas 2 through M receivedby processor 106 when detecting a signal in antenna 1 may be attenuatedby power coupling factors 118 L₂ through L_(M). The factors L₂ throughL_(M) correspond to the proportion of the incident powers received byantennas 2 through M that will show in the antenna channel 112 ofantenna 1 because of the imperfect isolation in antenna switch 104. Thetotal estimated power received by processor 106 from antenna 1 isP₁=Q₁+Q₂L₂+ . . . +Q_(M)L_(M).

For illustration, when Q₁<<Q_(i)L_(i), i≠1 and that Q₂L₂ is dominant,the estimated received power received by processor 106 may reduced toP₁=Q₂L₂. In this case, a maximum power of interest at antenna 2 may begiven by P₁/L₂, which is the estimated received power of antenna 1divided by a measured power coupled factor between antennas 1 and 2.Therefore, the gain setting found for antenna 1 by the AGC through along dwell time may be backed-off for use in antenna 2 to allow for asignal whose power is as large as P₁/L₂ to be detected properly atantenna 2. The gain for antenna 2 may not need to be predetermined butmay be dynamically adjusted in each received frame. Repeating the sameexercise for cases where Q₃L₃, . . . , or Q_(M)L_(M) dominates, themaximum power of interest is P₁/L_(j), where L_(j)=max(L_(i), i≠1) isthe power coupling factor 118 for antenna j. Since L_(j) is known,backing-off the gain setting found for antenna 1 to allow for P₁/L_(i)to be detected properly at antenna j may also allow for P₁/L_(i), i≠j,1to be detected properly at antenna i. The gain setting for all antennasother than the starting antenna may be dynamically set as it isbacked-off from the gain setting found for antenna 1. If there issufficient time, the gain back-off may be implemented in more than onestep. In this regard, a time required to finish dynamic gain control ismuch less than a time required to run a full automatic gain control(AGC) on each of the antenna channels in receiver system 100.

FIG. 2A illustrates exemplary received powers by different antennas in areceiver system, in accordance with an embodiment of the invention.Referring to FIG. 2A, in this exemplary illustration the receiver system100 may be a two antenna system comprising antenna j and antenna i. Thereceiver system 100 may determine whether antenna j or antenna i may beselected as the best antenna for decoding the incoming frame or packetinformation. Antenna j receives a stronger received power than antenna i(Q_(i)<Q_(j)) and therefore receiver system 100 should select antenna jfor signal decoding.

FIG. 2B illustrates exemplary antenna dwell times, signal gain, andantenna selection in a receiver system in connection with selectiondiversity with dynamic gain control, in accordance with an embodiment ofthe invention. Referring to FIG. 2B, the receiver system 100, indetermining whether it should select antenna j or antenna i in FIG. 2Afor signal decoding, may first dwell on antenna j, if antenna j wasselected as the starting antenna. Once the signal is detected, the gainG_(j) may be determined for antenna j. The processor 106 may determinean estimated received power P_(j) for antenna j. The processor 106 maythen dwell on antenna i by notifying the antenna switch 104 to selectantenna i for detection. The gain G_(i) for antenna i may be set tocorrespond to the gain G_(j) or lower for antenna j or to apredetermined value. In that case, the processor 106 may determine anestimated received power for antenna i that may be lower than theestimated received power for antenna j. After dwelling on both antenna jand antenna i, the processor 102 may correctly select antenna j as theone with the strongest signal, notify the antenna switch 104 to selectantenna j, and use the signal from antenna j for decoding the packetbeing received in the current information frame. As long as the antennawith the strongest signal is the same as the antenna that the receiversystem 100 selects as the starting antenna, setting the gain of allfollowing antennas to correspond to the gain of the first antenna mayresult in the correct antenna selection.

FIG. 3A illustrates exemplary received powers by different antennas in areceiver system, in accordance with an embodiment of the invention.Referring to FIG. 3A, in this exemplary illustration the receiver system100 may be a two antenna system comprising antenna j and antenna i. Thereceiver system 100 may determine whether antenna j or antenna i may beselected as the best antenna for decoding the incoming frame or packetinformation. Antenna j receives a stronger received power than antenna i(Q_(i)<Q_(j)) and therefore receiver system 100 should select antenna jfor signal decoding.

FIG. 3B illustrates exemplary antenna dwell times, signal clipping, andantenna selection in a receiver system in connection with selectiondiversity with dynamic gain control, in accordance with an embodiment ofthe invention. Referring to FIG. 3B, the receiver system 100, indetermining whether it should select antenna j or antenna i in FIG. 3Afor signal decoding, may first dwell on antenna i, if antenna i wasselected as the starting antenna. Once the signal is detected, the gainG_(i) may be determined for antenna i. The processor 106 may determinean estimated received power P_(i) for antenna i. The processor 106 maythen dwell on antenna j by notifying the antenna switch 104 to selectantenna j for detection. The gain G_(i) for antenna j may be set tocorrespond to the gain G_(i) for antenna i or to a predetermined value.Such case may occur, for example, if dynamic gain adjustment only usesthe gain of antenna i and does not use other signal quality metrics insetting the gain in antenna j. Because the signal in antenna i may beweaker than that in antenna j, if the gain G_(i) for antenna j is set tocorrespond to the gain G_(i) or larger, the signal in antenna j may beclipped and processor 106 may not be able to accurately determine theestimated received power P_(j) for antenna j. The processor 106 may dropantenna j because it could not determine its estimated received powerand may select antenna i for signal decoding. By setting the gain in allfollowing antennas after the starting antenna to correspond to a reducedportion of the gain of the starting antenna, the receiver system 100 mayavoid signal saturation and be able to select the correct antenna forsignal decoding.

FIG. 3C illustrates exemplary antenna dwell times, dynamic gain control,and antenna selection, in accordance with an embodiment of theinvention. Referring to FIG. 3C, the receiver system may dynamicallycontrol the gain G_(j) to be applied to antenna j by applying a gainG_(i)L_(j), where L_(j) is the power coupling factor between antenna jand antenna i. The coupling power factor L_(j) may be used to reduce thegain and to guarantee that signal saturation may not result in theincorrect selection of the best antenna for signal decoding. Because thecoupling power factors 118 may be known from the antenna switch 104specification or may be measured prior to the operation of receiversystem 100, they may be stored in memory 108 and may be used by theprocessor 106 to dynamically control the gain in all following antennasafter the starting antenna. The processor 106 may apply a gainG_(S)L_(j), where G_(s) corresponds to the gain of the starting antenna,whichever one may be selected as the starting antenna by processor 106,and L_(j) corresponds to the power coupling factor between the currentdwelling antenna j and the starting antenna. When the processor dwellson a following antenna k, and the estimated received power of antenna kcorresponds to the strongest signal, the processor 106 may selectantenna k as the best antenna and may apply a gain G_(k)L_(i) to antennai, where G_(k) corresponds to the gain of antenna k and L_(i)corresponds to the power coupling factor between the current dwellingantenna i and the best antenna or antenna k.

FIG. 4A illustrates exemplary received powers by different antennas in areceiver system, in accordance with an embodiment of the invention.Referring to FIG. 4A, in this exemplary illustration the receiver system100 may be a two antenna system comprising antenna j and antenna i. Thereceiver system 100 may determine whether antenna j or antenna i may beselected as the best antenna for decoding the incoming frame or packetinformation. Antenna j and antenna i receive the same incoming power(Q_(i)=Q_(j)) and therefore receiver system 100 may select eitherantenna j or antenna i for signal decoding.

FIG. 4B illustrates exemplary antenna dwell times, dynamic gain control,and antenna selection, in accordance with an embodiment of theinvention. Referring to FIG. 4B, the receiver system 100, in determiningwhether it should select antenna j or antenna i in FIG. 4A for signaldecoding, may first dwell on antenna i, if antenna i was selected as thestarting antenna. Once the signal is detected, an AGC is applied toantenna i to determine the gain G_(i) for antenna i. The processor 106may determine an estimated received power P_(i) for antenna i after theAGC has settled. The processor 106 may then dwell on antenna j bynotifying the antenna switch 104 to select antenna j for detection. Thegain G_(j) for antenna j may be set by processor 106 to correspond toG_(i)L_(j), where G_(i) corresponds to the gain of antenna i and L_(j)corresponds to the power coupling factor between antenna j and antennai. While the processor 106 may compensates for the lower applied gain inantenna j and may determine that the received power is the same in bothantenna j and antenna i, the processor 106 may select antenna i overantenna j in this case because antenna j may be more susceptible thanantenna i to transients signals, to capacitative or inductive coupling,and/or to other noise sources. Because the starting antenna maygenerally have longer dwelling times and an AGC may be used, thestarting antenna may, in general, be less susceptible than otherantennas to transients signals, to capacitative or inductive coupling,and/or to other noise sources.

FIG. 5 is a flow chart illustrating exemplary steps that may be utilizedin a receiver system for antenna selection with dynamic gain control, inaccordance with an embodiment of the invention. Referring to FIG. 5, thereceiver system 100 may start receiving a new frame in step 502. Theprocessor 106 may select in step 504 the starting antenna based on apredetermined criteria, based on a random selection, and/or based onhistory of prior antenna selection. The starting antenna may be selectedbased on a different selection criterion from frame-to-frame. In step506, the processor 106 may dwell on the starting antenna for apredetermined amount of time or until an event may indicate completionof dwelling in that starting antenna. In step 508, the processor 106 maydetermine whether the desired signal has been detected in the startingantenna. If the signal has not been detected after a certain amount oftime, or under other performance criteria, the processor 106 may selecta different starting antenna and return to step 504. If the signal hasbeen detected within predefined performance constraints, the processor106 may proceed to step 510. In step 510, the gain G_(s) of the startingantenna may be determined by AGC or by the processor 106. In step 512,the processor 106 may determine the estimated received power of thestarting antenna or it may determine the received power of the startingantenna. In step 514, the processor 106 may collect information on thegain G_(s) of the starting antenna, the estimated power of the startingantenna, and/or the received power of the starting antenna, and store itin memory 108.

In step 516, the processor 106 may determine whether the signal qualitymetric at the starting antenna is strong enough. The signal qualitymetric may refer to the received power, Q, or to the estimated receivedpower, P. To determine whether the signal quality metric is strongenough, the processor may compare the signal quality metric from step512 to a threshold level. For example, if the signal in the startingantenna is at least 40 dB above noise, then the signal may be strongenough for detection and decoding. If the signal quality metric isdetermined to be adequate, then the processor 106 may proceed to step518. In step 518, the processor 106 may determine if the signal qualitymetric in the starting antenna meets a selection criteria so that thestarting antenna may be selected as at least one of the antennas thatmay be used for signal detection and signal decoding. The selectioncriteria may depend, for example, on the gain setting for the antenna,on the location of the antenna, on the number of antennas that may beselected, on the number or antennas that may have been dwelled on thusfar, on the history of prior antenna selection, on the history of priorcollected antenna information, and/or on an optimal amount of time thatthe receiver system 100 to detect and decode an antenna signal. If theantenna meets the selection criteria, the processor 106 may proceed tostep 520 and decode the incoming signal from the selected antenna in thecurrent frame. After decoding, the processor 106 may proceed back tostep 502 and start a new information frame.

If in step 516 the signal quality metric in the starting antenna was notadequate to meet or exceed the threshold level, the processor 106 mayproceed to step 522 where it may select a current dwelling antenna basedon prior antenna selection history, based on a random selection, and/orbased on a predetermined dwelling schedule. The processor 106 may applya gain to the current dwelling antenna in step 524. The gain may dependon the collected gain, collected power information, and/or on the powercoupling factors of all antennas dwelled on by the processor 106 thusfar. In the case where the only antenna dwelled on is the startingantenna, the gain in step 524 may depend on the collected gain,collected power information in step 514 and/or on the power couplingfactor between the current dwelling antenna and the starting antenna.For example, the gain setting may be G_(S)L_(d), where L_(d) correspondsto the coupling factor between the current dwelling antenna and thestarting antenna. In step 526, the processor 106 may determine thesignal quality metric of the current dwelling antenna. The signalquality metric may correspond to the estimated received power, P, or thereceived power, Q, of the current dwelling antenna. In step 528, theprocessor 106 may collect the antenna performance information and storeit in memory 108.

In step 530, the processor 106 may determine whether the signal qualitymetric of the current dwelling antenna is adequate. The signal qualitymetric may refer to the received power, Q, or to the estimated receivedpower, P. To determine whether the signal quality metric is adequate,the processor may compare the signal quality metric from step 526 to athreshold level. The threshold level in step 530 may be the same as thethreshold level in step 516 or may be different. If the signal qualitymetric is not adequate, the processor 106 may return to step 522 andselect a different current dwelling antenna from the remaining antennasin the receiver system 100. If the signal quality metric is adequate,the processor 106 may proceed to step 518 and determine whether theantenna performance meets or exceeds a specified selection criteria. Ifthe current dwelling antenna meets or exceeds the selection criteria instep 520, then the processor 106 may proceed to step 520 and then to anew frame in step 502.

In one aspect of the present invention, carrier detection and fullautomatic gain control (AGC) may be performed on a starting antenna,whereas only dynamic gain control may be performed while dwelling on thesecond and subsequent antennas. Accordingly, the signal received on thestarting antenna may first be verified as a valid frame before its poweris estimated. However, for any of the remaining antennas, timeconstraints may only permit power estimation and no carrier detection.Furthermore, noise, signal transients, and offsets may corrupt the powerestimates and may lead to an increase in the probability of selectingthe wrong antenna as the receive antenna, especially in cases where thereceived signal powers of all antennas are similar. For example, antennaselection without biasing may be accomplished by selecting an antennawith a highest power estimate. However, the power may be misestimated.Even though a signal may be coming in at a given actual power, animpaired version may be received by an antenna and a misestimated totalpower may be obtained. As a result, during antenna selection, instead ofobtaining actual receive powers Q_(i) for an antenna i, an estimatedpower P_(i) may be obtained, where P_(i) may include impairments so thatP_(i) is higher or lower than the actual receive power Q_(i).

FIG. 6 is a graphical depiction of antenna selection without a bias,which may be utilized in connection with an embodiment of the invention.Referring now to FIG. 6, the graphical depiction 600 illustrates theactual receive powers Q_(i) and the estimated power P_(i) for antenna ion the x-axis, and actual receive power Qj and estimated power Pj forantenna j on the y-axis. The 45-degree line s1 divides the quadrant inthe graphical depiction 600 into two equal sections, namely section Aand section B, respectively.

Antenna selection for the antennas i and j may be accomplished bycomparing their estimated powers P_(i) and P_(i), respectively. If theestimated power values for antennas i and j are located below line s1and in section B, this may indicate that the estimated power for antennai is bigger than the estimated power for antenna j. Therefore, antenna imay be selected in an antenna selection process. If on the other handthe estimated power values for antennas i and j are located above lines1 and in section A, this may indicate that the estimated power forantenna j is bigger than the estimated power for antenna i. Therefore,antenna j may be selected in an antenna selection process.

The actual receive powers Q_(i) and Q_(j) for antennas i and j, however,may be different from the respective estimated power values P_(i) andP_(i). For example, the graphical depiction 600 illustrates theestimated power values (P_(i); P_(i)) and the actual receive powervalues (Q_(i); Q_(i)) where (P_(i); P_(i)) is in section A and(Q_(i)Q_(j)) is in section B. In this case, Q_(i) is larger than Q_(j).However, because of mis-estimations due to noise, for example, theestimated power value P_(i) is smaller than P_(j). As a result, theantenna j may be incorrectly selected over antenna i, even thoughantenna i may have a higher power.

To prevent corrupted power estimates from causing selection of anincorrect antenna, the antenna selection may be biased towards a targetantenna, for example. Biasing an antenna selection may safeguard againstselecting the wrong antenna for signal processing in the presence ofnoise, transients, and offsets when all the power estimates are similar.

In another aspect of the present invention, antenna selection diversitymay be accomplished with dynamic gain control. After a starting antennais selected, it may be biased by shifting the selection region by Xunits, for example. In this way, a new second antenna may be selected asa target antenna only if the estimated power of the second antenna isgreater than the power of the first selected antenna plus the bias Xunits. For example, there may be automatic gain control and carrierdetermination for a first antenna. For any subsequent antennas, therespective power values may be misestimated because of transients and/ornoise, for example. In order for any subsequent antenna to be selectedfor receiving data, it may not be enough that the estimated power of thesubsequent antenna is larger than the estimated power of the firstantenna. By adding X units, the estimated power for a subsequent antennamay be required to exceed the estimated power of the first antenna andthe added bias X, in order for the second antenna to be selected.

FIG. 7 is a graphical depiction of antenna selection with a bias, inaccordance with an embodiment of the present invention. Referring now toFIG. 7, the graphical depiction 700 illustrates the actual receivepowers Q, and the estimated power P_(i) for antenna i on the x axis, andactual receive power Qj and estimated power Pj for antenna j on the yaxis. The 45-degree line s2 divides the quadrant in the graphicaldepiction 700 into two sections, section C and section D, respectively.In order to accomplish biasing of an antenna selection, the dividingline s2 may be shifted or changed in angle or shape in comparison toline s1 in order to account for a certain amount of bias. For example,antenna i may be biased by shifting the line s2 upwards, and antenna jmay be biased by shifting the line s2 to the right. The change in shape,angle or location of line s2 may be represented as a modification to, orbiasing of, the signal quality estimates.

Antenna selection for the antennas i and j may be accomplished bycomparing their estimated powers P_(i) and P_(i), respectively. If theestimated power values for antennas i and j are located below line s2and in section D, this may indicate that the modified estimated powerfor antenna i is bigger than the modified estimated power for antenna j.Therefore, antenna i may be selected in an antenna selection process. Ifon the other hand the estimated power values for antennas i and j arelocated above line s2 and in section C, this may indicate that theestimated power for antenna j is bigger than the estimated power forantenna i. Therefore, antenna j may be selected in an antenna selectionprocess.

The graphical depiction 700 illustrates a bias of X units towardsantenna i, since the line s2 is shifted upwards by X units. Antenna imay be initially selected as a target antenna, for example by utilizingantenna selection diversity with automatic gain control. By biasingantenna i by X units, the actual receive power values (Q_(i); Q_(j)) andthe estimated power values (P_(i); P_(j)) may all be located in the samesection D. In this way, antenna i may be selected even though antenna jmay be misestimated with higher power.

In one aspect of the invention, the following equation may be utilizedto determine whether a biased antenna i may remain as a selectedantenna:

${P_{i,{dB}} + X_{dB}} > {\max\limits_{j \neq 1}( P_{j,{dB}} )}$Antenna i may be selected as the target antenna from a group ofantennas, unless there is at least one other antenna j, whose powerP_(j) is at least X dB greater than that of antenna i. In a anotheraspect of the present invention, a setting of X dB=0 may turn off thebiasing towards antenna i and a setting of X dB<0 may bias away fromantenna i.

In another aspect of the invention, the bias value of X dB may beselected dynamically or as a fixed value, depending on an expectedamount of noise, for example. For weak signals, for example,misestimating errors may be in the order of 1 dB. In this case, thebiasing value X may be selected larger than 1 dB. The bias value X maybe dynamically changed, if the error margin in estimated power signalsis monitored.

FIG. 8 is a flow diagram of an exemplary method 800 for selecting asignal path, in accordance with an embodiment of the invention.Referring to FIG. 8, at 801, a signal quality metric may be determinedfor each of a plurality of signal paths. At 803, the signal qualitymetric for each of the plurality of signal paths may be modified. At805, at least one signal path may be selected based on one or moremodified signal quality metric.

Accordingly, the invention may be realized in hardware, software, or acombination of hardware and software. The present invention may berealized in a centralized fashion in at least one computer system, or ina distributed fashion where different elements are spread across severalinterconnected computer systems. Any kind of computer system or otherapparatus adapted for carrying out the methods described herein issuited. A typical combination of hardware and software may be ageneral-purpose computer system with a computer program that, when beingloaded and executed, controls the computer system such that it carriesout the methods described herein.

The invention may also be embedded in a computer program product, whichcomprises all the features enabling the implementation of the methodsdescribed herein, and which when loaded in a computer system is able tocarry out these methods. Computer program in the present context meansany expression, in any language, code or notation, of a set ofinstructions intended to cause a system having an information processingcapability to perform a particular function either directly or aftereither or both of the following: a) conversion to another language, codeor notation; b) reproduction in a different material form.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A method, comprising: determining a signalquality metric for each of a plurality of signal paths, each of theplurality of signal paths corresponding to a respective one of aplurality of antennas; modifying the determined signal quality metricfor one of the plurality of signal paths; and selecting a subset of theplurality of signal paths for receiving a signal based at least in parton the determined signal quality metrics, the selecting being biasedbased at least in part on the modified signal quality metric.
 2. Themethod of claim 1, wherein the signal quality metric comprises asignal-to-interference ratio.
 3. The method of claim 1, wherein thesignal quality metric comprises a power level characteristic.
 4. Themethod of claim 1, wherein the signal quality metric comprises a packeterror rate characteristic.
 5. The method of claim 1, wherein the signalquality metric comprises a bit error rate characteristic.
 6. The methodof claim 1, wherein the signal quality metric comprises a propagationchannel characteristic.
 7. The method of claim 1, further comprisingcycling through at least one of the plurality of signal paths.
 8. Themethod of claim 1, wherein the modifying comprises increasing thedetermined signal quality metric for the one of the plurality of signalpaths by a fixed amount or a predetermined amount.
 9. The method ofclaim 1, wherein the modifying comprises dynamically changing thedetermined signal quality metric for the one of the plurality of signalpaths.
 10. The method of claim 1, wherein the modifying comprisesdecreasing the determined signal quality metric for the one of theplurality of signal paths by a fixed amount or a predetermined amount.11. The method of claim 1, wherein the selecting comprises selecting asignal path with a signal quality metric greater than the modifiedsignal quality metric.
 12. The method of claim 1, wherein the selectingcomprises selecting a signal path with a signal quality metric less thanthe modified signal quality metric.
 13. A system, comprising: circuitryconfigured to: determine a signal quality metric for each of a pluralityof signal paths, each of the plurality of signal paths corresponding toa respective one of a plurality of antennas; modify the determinedsignal quality metric for each of a subset of the plurality of signalpaths; and select at least one of the plurality of signal paths forreceiving a signal based at least in part on the determined signalquality metrics, the selecting being biased based at least in part onthe modified signal quality metrics.
 14. The system of claim 13, whereinthe signal quality metric comprises a power level characteristic. 15.The system of claim 13, wherein the signal quality metric comprises apacket error rate characteristic.
 16. The system of claim 13, whereinthe signal quality metric comprises a bit error rate characteristic. 17.The system of claim 13, wherein the signal quality metric comprises apropagation channel characteristic.
 18. The system of claim 13, whereinthe modifying comprises increasing the determined signal quality metricsfor the subset of the plurality of signal paths.
 19. The system of claim13, wherein the modifying comprises decreasing the determined signalquality metrics for the subset of the plurality of signal paths.
 20. Asystem, comprising: circuitry configured to: determine a signal qualitymetric for each of a plurality of M signal paths corresponding to Mantenna inputs; modify the determined signal quality metric for each ofa subset of the plurality of M signal paths; and select at least one ofthe plurality of signal paths for receiving a signal, the selectingbeing biased based at least in part on the modified signal qualitymetrics.